Gear type rotary pump and motor hydraulic transmission



GEAR TYPE ROTARY PUMP AND MOTOR HYDRAULIC TRANSMISSION Filed July 20, 1944 4 Sheets-Sheet 1 INVENTOR flak/(v.3 5v CARROLL arch s, 1949. a CARROLL ma ma GEAR TYPE R Rl PU AN OTOR HYDRAU 1 TRAN 55 Filed July 20, 1944 4 Sheets-Sheet 2 ENTO Mae/as .CAK/P L March & 3949., M. B. cARRQLL. 2., $53,95@

GEAR TYPE ROTARY PUMP AND MOTOR HYDRAULIC TRANSMISSION Filed July 20, 1944 4 Sheets-Sheet 5 8, 'i fr o M. B. CARROLL 2,

GEAR TYPE ROTARY PUMP AND MOTOR HYDRAULIC TRANSMISSION 4 Sheets-Sheat 4 Filad July 20,, 194A A T N E Y Patented Mar. 8, 1949 GEAR TYPE ROTARY PUMP AND MOTOR HYDRAULIC TRANSMISSION Morris B. Carroll. Westiield, N. J., assignor oi twenty-five per cent to H. Dorsey Spencer,-New

York, N. Y.

Application July 20, 1944, Serial No. 545,856

7 Claims. 1

This invention relates to hydraulic transmissions and particularly to hydraulic transmissions of the type in which a positive displacement pump, associated with the driving mechanism, supplies fluid under pressure to a positive displacement hydraulic motor associated with the driven mechanism and in which the speed of the motor and the torque delivered by it are varied primarily either by varying the displacement of the pump at constant speed or by varying the displacement of the motor at constant pump displacement or by simultaneously varying the displacements of both.

A general object of the present invention is to provide a hydraulic pump or motor, having particular utility in hydraulic transmissions of the aforementioned type, which is simple in construction and efficient in operation and which is provided with simple, positive and eflioient means for effecting an desired variations of its speed and torque ratios between their maximum and minimum values.

More particularly the invention aims so to interconnect a pump and a motor of like design to form a hydraulic transmission operating in such manner that as the capacity of the pump is increased the capacity of the motor is proportionately decreased, and vice versa, thus amplifying the variations in speed. To this end the invention is directed to a hydraulic transmission in which a Pump and a motor, each having two rtary intergeared pistOIls provided with close-fitting sheaths relatively slidable axially to expose in effective position more or less of the piston faces and each mounted in a casing, having intake and discharge ports and piston bearings, in such manner that the casing provides space for simultaneous axial movement of one sheath, while its piston maintains its position in said casing, and for axial movement of the other piston, while its sheath maintains its position in said casing, are so interconnected that the axially movable piston of the motor is connected to and movable axially with but rotatable independently of the axially movable piston of the pump and that the axially movable sheath of the pump is connected to and movable axially with but rotatable independently of the axially movable sheath of the motor.

An important feature of the invention is the possibility of combining with the hydraulic transmission a positive clutch for direct connection of the driving and driven parts when the desired speed has been attained.

Other objects and important features of the invention will appear from the following description and claims when considered in connection with the accompanying drawings, in which- Figure 1 is a plan view, with some parts shown in section, of a hydraulic pump or motor em- 2 bodying novel features of the present invention, the top half of the pump or motor casing being removed;

Figure 2 is a section on the line 2-2 of Figure 1;

Figure 3 is a section on the line 33 of Figure 1;

Figure 4 is a section on the line 4-4 of Figure 3;

Figure -5 is a plan view with some parts shown in section of a hydraulic pump and a hydraulic motor, each embodying important novel features of the present invention and both so included in a single housing as to be operable in unison to increase or decrease the displacement of one, while at the same time a substantially corresponding decrease or increase in the displacement of the other is effected, whereby the unit thus provided may be substituted for the transmission gear box of a motor vehicle or other variable speed transmission device;

Figure 6 is a section on the line 6-6 of Figure 5;

Figure '7 is a section on the line 1-1 of Figure 5;

Figure 8 is a detail section in reduced scale illustrating the manner of mounting the pump and motor gears on a common slidable shaft;

Figure 9 is a diagrammatic view showing a transmission, such as illustrated in Figure 5, incorporated in a motor vehicle;

Figure 10 is a diagrammatic view showing how the relative movements of the gears and their associated sheaths, to vary the displacement of the pump or motor, may be eifected hydraulically, and

Figure 11 is a detail of the hydraulic means of Figure 10 showing the 2-way valve in its other position.

In Figures 1 to 4 inclusive, which illustrate a single unit of the combination to which the invention particularly relates and Which'may be used either as a variable displacement hydraulic pump or as a hydraulic motor of variable displacement, the pump or motor shown is of the gear typ Although, for convenience of illustration, the gears shown have the faces of their teeth extending parallel to the gear axis, it will be understood that the invention is not limited to gear pumps necessarily having teeth of the illustrated character, since it is equally applicable to any type of gear pump in which a sheath may be caused to slide lengthwise of the gear teeth in a direction parallel to the gear axis.

As herein illustrated, the pump or motor comprises a housing Or casing which may be formed in two pieces, 2 and l, having lips or flanges Ii and 8 for receiving bolts or screws It) by which the two parts of the housing or casing are secured together. The housing or casing is also provided with an intake port l2 and a discharge port l4 for the liquid which serves to operate, or which is operated upon by, the motor or pump.

The pump pistons, or motor rotors, comprise intermeshing gear wheels I6 and I6, the gear wheel [6 being arranged to turnfreely on and to slide lengthwise of a stationary shaft 28 having its ends mounted in the pump or motor housing and preferably not extending therethrough, while the gear I8 is keyed to the shaft 22 to turn therewith and is fixed in its lengthwise position thereon, the shaft 22 having one bearing 24 entirely within one wall of the pump or motor housing while the other bearing is provided with a, stuffing box 26 and gland 28 to permit extension of the shaft through the opposite wall of the housing for connection either with a driving part or with a part to be driven, according to whether or not the device is to be used as a pump or as a motor.

To provide for varying the displacement of the pump or motor, each of the gears l6 and I8 is provided with a complementary sheath having inwardly extending teeth which fit between the teeth of the associated gear so that by sliding the sheath'lengthwise of the axis of the gear or sliding the gear lengthwise of the axis of the sheath the total amount of piston surface or impact surface of the gear which is exposed may be varied. It will be obvious that it is practically essential for efiicient operation that the variations in the piston surfaces of the two intermeshed gears of the gear pump or motor be varied substantially equally and in the same direction so that the torque will be equal on the two gears. To secure this effect the invention provides for sliding one of the sheaths over its associated gear to cover or uncover more or less of the piston faces of the gear and at the same time to slide the other gear into or out of its associated sheath to cover or uncover more or less of its piston faces, the last mentioned gear also sliding relatively to the gear which is fixed against sliding movement so that the engaging areas of the two gears will be equal. As herein illustrated, and particularly as shown in Figure 1 of the drawings, the sheath 38 for the gear l6, which necessarily turns with the gear I6, is fixed against sliding movement in the pump or motor housing 2, 4. The illustrated means for providing for turning movement of the sheath 38 While preventing its sliding movement comprises a peripheral groove 32 in the sheath 38 into which fits a tongue 34 formed on the inside of the housing.

The sheath 36 for the gear I 8, which is arranged to move lengthwise of the axis of the gear l6, to sheath or unsheath more or less of the piston faces of the teeth 38 of the gear l8, at the same time that the gear I6 is being moved lengthwise of its shaft 28 to unsheath or sheath more or less of the piston-faces of the teeth 48 of said gear l6 by withdrawing them from or inserting them within the sheath 38, is also arranged to turn with its associated gear while maintaining its adjusted position in the housing 2, 4. To this end the sheath 36 is also provided with a groove 42 which engages a tongue 44 in a concave recess 46 in a block 48. The block 48 is connected to and slides with the gear 16 on the shaft 28 and fits closely within the housing so that it forms a closure for one end of each of the interstices between the non-engaged gear teeth 48 of the gear l6. The connection between the block 48 and gear l6 permits the gear I 6 to turn on the shaft 28 while the block 48 is held against rotation, as hereinafter more fully described.

The housing 2, 4, is so formed that a fixed block 58, similar to the slidable block 48 but forming an integral part of the housing and through which the shaft 22 extends and in which it has a part of its bearing, forms a stationary closure for the interstices between the non-engaged teeth 38 of the non-slidable gear [8. This fixed abutment closure 58 for the interstices between the non-engaged teeth 38 of the gear l8, likethe sliding block 48, has a concave recess 52 to accommodate the rotating sheath 38 for the gear I6. The fixed block 58 also has a. tongue or rib 53 entering the groove 32 of sheath 38. To form a peripheral closure for the interstices between the teeth 38 of the ear l8 that will be effective in all positions of the sheath 36, a segment 54 of a cylinder is provided, of such axial length that it provides throughout its angular extent a peripheral closure for the interstices between the teeth 38 of the gear l8 in any adjusted position of the sheath 36, this segment being received in a correspondingly shaped recess 56 between the fixed block 58 and the surrounding portion of the housing. As shown in Figure 2, the segment 54 needs to extend only to the vicinity of the port l2 at one end of its. angular extent and to the vicinity of the port l4 at the other end thereof.

To provide for movement of the segment 54 with the sheath 36, the sheath 36 may be formed with a second groove 58, the outer wall 68 of which is of reduced diameter so that a tongue 62 on the segment 54 may fit into the groove 58 on the sheath 36 and the outer wall 68 of the groove 58 may fit into a groove 64 in the sheath 54 thus connecting the segment 54 to the sheath 58 for sliding movement in respect to the gear I8, while at the same time permitting the sheath 36 to turn with the gear l8 within the segment 54. It will also be noted, as above pointed out, that the sheath 36 forms a closure for the sides of the interstices between the gear teeth 38 which are opposite to the sides closed by the block 58 and that the sheath 38 forms a closure for the sides of the interstices between the teeth 48 of the gear l6 which are opposite to those closed by the block 48 which slides with the gear I6. The peripheral closure for the interstices between the teeth 48 of the gear [6 is constituted by the housing itself, this being made possible by the fact that the gear 16 slides withinits peripheral enclosure while in the case of the gear l8 the peripheral closure slides over the gear thus making necessary the use of the segment 54.

To permit displacement of' the liquid within the housing 2, 4, when the relative movement of the gears and sheaths of the gear pump or motor is effected to vary the capacity of the pump or motor, by-passes are provided in the housing 2, 4. to permit the liquid between the outer faces of the block 48 and the sheath 36 on the one hand and the inner wall of the housing 2, 4 on the other to move from this space into the space between the'opposite wall of the housing and the inside of the sheath 38 and also into the space vacated by the segment 54 or vice versa. As herein shown, a by-pass 66, formed in the housing section 2, has one end communicating with the space between the outer faces of the block 48 and sheath 36 on the one hand and the inner wall of the housing on the other hand and its other end communicating with the interior of the sheath 38. A branch 68 of the by-pass 66, formed in the stufllng-box wall of the housing, communicates with the recess 56 which receives the segment 54.

The relative movement of the gears and sheaths may be efl'ected either mechanically or hydraulically. If the movement is to be effected mechanically, a rod I8, extending through the wall of the housing 2, 4 opposite to that in which the stufling box 28 is formed, may be connected to the block 48 so that sliding movement of the rod I8 through the housing wall will efiect movement of the block 48 and with it the gear I8 to cause more or less of the piston faces of the gear I8 to be exposed, the block 48, by reason of the projection of the tongue 44 into the groove 42 of the sheath 36, carrying with it the sheath 38 and thus causing a corresponding covering or exposure of the piston or impact faces of the teeth of the gear I8.

In Figure 10 is shown a simple arrangement for effecting the relative shifting of the gears and sheaths hydraulically. In Figure 10, instead of lay-passing the liquid from one side of the housing 2, 4 to the other through the bypass 68, the opening into the space between the outer faces of the block 48 and sheath 36 and the inner wall of the housing is connected to a conduit I2 leading to a 2-way valve I4 and th opening into the space between the other wall of the casing and the inside of the sheath 38 is connected with a conduit 18 also leading to the 2-way valve 14, this 2-way valve I4 also having a connection I8 to the discharge conduit 88 from the pump or motor and another connection 82 to the input conduit 84 to the pump or motor. By turning the valve I4 so that its pass 85 connects the conduit I2 with the discharge conduit 88 and its pass 88 connects the conduit IS with the conduit 82 and the intake conduit 84, if the device is operating as a pump, pressure will be exerted to effect a shifting upwardly in Figure 10, thus reducing the volumetric capacity or displacement of the pump. If the valve I4 be turned to the position shown at the right in Figure 11 so that the pass 86 connects the conduit 88 with the conduit 18 and the pass 88 connects the conduit i2 with the conduit 82 and intake conduit 84, then the pressure is exerted in a direction to cause a shift downward, with the result that more of the piston faces of the teeth of the gear I8 and I8 are uncovered and the volumetric capacity or displacement of the pump or motor is increased.

In Figures 5 to 8 inclusive, the invention is shown as embodied in a combination of a variaole displacement pump and a variable displacement motor arranged within a common housing. Such a combined unit may conveniently take the place of the usual variable speed transmission for motor vehicles, lathes and other machinery where gradual variations in speed and torque are desired.

Figure 9 illustrates diagrammatically this form of the invention substituted for the usual variable speed transmission of a motor vehicle.

For convenience in relating the parts of the embodiment of the invention illustrated in Figures 5 to 8 inclusive to the parts of the embodiment of the invention illustrated in Figures 1 to 4 inclus ve, the parts so far as possible will be given similar reference numerals, the numbers of the duplicate parts being primed. Referring to F gure 5 two ea s IR and I8 are so mounted on a hollow shaft 28' slidable on a shaft 2| extending into but not through the two sides of the casing or housing that these gears may slide with said hollow shaft 28', together with a block 48' also mounted on the hollow shaft but not rotatable thereon, said block 48' serving to close one side of the interstices between the nonengaged gear teeth 48 and 48'. As the two gears I8 and I8 slide, together with their common block 48', with the hollow shaft 28' on the shaft 2I', if the sliding movement be downward in Figure 5, the gear I8 will slide out of its sheath 38 and the gear I6 will slide into its sheath 38', these sheaths being mounted. as in the embodiment of the invention illustrated in Figures 1 to 4, to turn with the gears but being held by tongues 34 and 34' against movement along the axis of the shaft 2|.

The gears I8 and I8, which mesh respectively with the gears I6 and I6, are fixed, as in the form of the invention illustrated in Figures 1 to 4 inclusive, against movement lengthwise of their respective shafts, the gear I8 being connected to the power driven shaft 22' which corresponds to the shaft 22 of the form of the invention illustrated in Figures 1 to 4 inclusive. The shaft 22' may be connected to a source of power, such as the motor of a motor vehicle, thus making that part of the combined unit which comprises the gears I8 and IS the pump element of the unit.

The gear I8 is connected to a shaft I48, constituting an element of the mechanism to which power is to be transmitted, such, for example, as the driving shaft of a motor vehicle.

As in the form of the invention illustrated in Figures 1 to 4 inclusive, the sheath 38 for the gear I8 is adapted to slide over the gear I8 to cover or uncover more or less of the piston faces of the teeth 88 of the gear I8, a tongue 44 on block 48 entering the groove 42 in the sheath 38 to cause the sheath 38 to move with the block 48'. Simi- 5 larly, a sheath 38' for the gear I8 has a groove 0 Figure 5 of the drawings both the sheath 38 and the sheath 36' will move downwardly with it, thus uncovering more of the piston faces of the teeth 38 of the gear I8 and covering up more of the piston faces of the teeth 38' of the gear I8. At the same time the gear IE will be moved out of its sheath 38 thus uncovering more of the piston faces of the teeth 48 of this gear and the gear I6 will be moved into its sheath 38 thus covering up more of the piston faces of the teeth 48'. The result will be that as the volumetric capacity or displacement of the pump, made up of the gears l8 and I8, is increased there will be a corresponding decrease in the volumetric capacity or displacement of the motor made up of the gears I6 and I8. When the block 48' moves upwardly in Figure 5, the reverse operation will take place and the volumetric capacity or displacement of the motor will be increased while the volumetric capacity or displacement of the pump is being decreased. This will provide for a wide variation in adjustment of the speeds at which the motor I6, I8 is driven by the pump I6, I8.

When, for example, a transmission of this type is used in a motor vehicle, it is usually desirable, when the vehicle has reached a certain speed, to effect a direct driving connection between the motor and the vehicle driving shaft, that is, between the shaft 22' here shown and the shaft I48. In order to provide for such direct drive in the embodiment of the invention illustrated in Figures 5 and 6, a clutch is provided, one member of which is connected to the shaft 22' and the other member of which is connected to the shaft I48. As herein shown, the male member I42 of a conical clutch is carried on a sleeve I 44 slidable on but keyed to the shaft 22 to turn therewith. At its end remote from the clutch member 42 the sleeve I44 is provided with an annular groove I46, in an enlargement of the sleeve, to receive a collar I48 by which connections may be made to clutch shifting mechanism. The female member I50 of the clutch is formed on the inside of the gear I8. To provide suitable support on the shaft I40 for the gear I8, to replace that lost by providing the clutch space, the gear I8 has a hub extension I52, keyed to an enlarged end on the shaft I 40. Moreover, to prevent endwise movement of shaft I40 an integral rib I54 thereon is received in a corresponding groove in the housing.

Further to insure centering of the clutch members I42 and I50, the end of the shaft 22' may extend into a bearing in the gear I8, the hub I52 of the gear I8 as well as the shaft I40, preferably having a bearing in the transmission housing, as shown.

As shown in Figure 6, assuming the gears I6 and I8 to constitute the pump, the pump has an intake or suction port I56 and a discharge or pressure port I58 and the motor has an intake or pressure port I60 and a discharge port I62. The pressure port I58 of the pump may be connected with the pressure or intake port I60 of the motor by suitable pipe connections.

Because of possible leakage past the moving parts and along the sliding connections it is usually desirable to have the adjustment so made that the displacement of the pump is slightly greater than that of the motor when the two are to be synchronized. For this reason it is preferable not to connect the motor discharge directly to the pump intake but to conduct the liquid from the motor back to the pump through a reservoir, which permits the desired flexibility in operation and which also may contain any necessary make-up liquid.

In Figure 9 of the drawings, a transmission of V the type shown in Figure is shown as incorporated in a motor vehicle having the usual differential I64 connected with the rear axles. The hydraulic transmission of the type shown in Figure 5 and indicated by the reference numeral I66, applied to its housing, takes the place of the usual automobile gear shifting transmission. The clutch sleeve I44 of this transmission is shown as having its collar I48 connected to a clutch pedal lever I68 by means of a pin I10 entering a slot I12 in the end of the pedal lever I68 to provide a lost motion connection for purposes hereinafter set forth.

To effect the shifti: ag of the pistons and sheaths of the transmission shown in Figure 5, which includes both a hydraulic motor and a hydraulic pump, a slide I14 is provided which comprises a bracket arm carrying plungers I16 and I18. The plunger I16 engages the outer edge of the segment 54 of the pump part of the transmission and the plunger I18 engages the outer edge of the segment 54' of the motor part of the transmission. With this arrangement it will be seen that if the slide I14 be moved downwardly in Figure 5 the displacement of the pump will be increased at the same time that the displacement of the motor is decreased and that if it be moved upwardly in Figure 5 the displacement of the motor will be increased at the same time that the displacement of the pump is decreased.

The slide I14 is shown in Figure 9 as connected to one arm of the cutch pedal lever I68, fulcrumed at I80, by means of a spring I82 of suflicient stiffness so that when the clutch lever is moved in a clockwise direction as shown in Figure 9 it will first move the slide I14 in a downward direction in Figure 5 against the tendency of a spring I84 to maintain it in a position in which the pump part of the transmission has no capacity at all. This will result in gradually increasing the displacement of the pump part of the transmission and decreasing the displacement of the motor part so that the shaft 22' will begin to drive the shaft I40 through the hydraulic connections, the speed of drive gradually increasing as the ratio of displacement of the pump part of the transmission to that of the motor part of the transmission is increased. This movement of slide I14 will continue until the stop member I86 on the slide I14 engages the adjustable stop I88 on the vehicle frame, this stop being adjusted to stop the slide I14 at the pointat which the speed of the driving shaft I 40 is substantially identical with the speed of the driving shaft 22 or, in other words, at the point where the pump and motor are rotating at the same speed. The lost motion connection provided by the pin I10 and slot I12 in the longer arm of the clutch pedal lever I 68 permits this initial movement of the lever I68 to efiect the change in ratio of the displacements of the pump and motor without movement of the clutch collar I 48 to effect the engagement of the clutch member I42 with the clutch member I50. Further movement of the clutch pedal lever I 68 in a clockwise direction will, however, engage the pin I10 with the left hand end of the slot I12 and effect the movement of the clutch member I42 into engagement with the clutch member I50, this engagement occurring after the shaft 22' and the shaft I40, to which the respective clutch members are connected, reach the same speed. A positive driving connection between the motor I90 and the driving shaft I92 is thus made.

In Figure 4 of the drawings is illustrated in detail one mode of connecting the block 48 to the gear I6 for axial movement together while permitting the gear I6 to turn freely. Roller bearings I1 facilitate free turning of gear I6. As shown in Figure 4, the block 48 is provided with a flanged hub extension I94 which provides a groove in which a split ring I96 may be received, the

split ring I96 being countersunk in the side face of the gear I6 and secured therein by screws I98, the heads of which are received in countersinks in the split ring I96. The flanged hub I94 of the block 48 is received in a recess in the gear I6 of sufiicient depth to permit the face of the main part of the block to fit close against one face of the gear. To permit access to the screws I98 for,

connecting the gear I6 to or detaching it from the block 48, openings 200 are provided through the block 48 which are closed against flow of the transmission liquid therethrough by screw plugs 202.

In Figure 8 is shown one method of securing the block 48' and the two gears I6 and I6 on the tween the discharge of the motor and the intake I of the pump in the form of the invention shown In this case a-ieaeco direct connection but through a storage reservoir such, for example, as the reservoir 2!!) shown in Figure 9.

Although the lever I68 is shown and described as a pedal lever, the movement thereof, of course, can be effected in any other manner. Moreover, although it is shown as moved positively into clutch engaging position, it will be understood that it can be arranged, as in the ordinary motor vehicle, to be spring-impelled into clutch engaging position and moved positively into clutch-releasing position, this movement carrying the slide i'lfi into the position in which it causes the pump capacity to be reduced to zero.

From the foregoing description it will be seen that the invention provides simple, positive and easily operable means for effecting any desired variations in the volumetric capacity or displacement of either a hydraulic pump or a hydraulic motor of the well-known and extensively used gear type. It will further be seen that the construction has a minimum of movable parts and of parts subject to wear, that its action is positive and that the variation effected is of definitely equal amounts in respect to both of the intergeared pistons.

What is claimed as new is:

1. In a hydraulic transmission, the combination with a rotary hydraulic pump or motor having two rotary intergeared pistons, each provided with a close-fitting sheath relatively slidable axially to expose in efiective position more or less of the piston faces, an enclosing casing having intake and discharge ports and in which bearings for said pistons are supported, said casing providing space for simultaneous axial movement of one s eath while its piston maintains its position in said casing and axial movement of the other piston while its sheath maintains its position in said casing, thereby to permit simultaneous covering or uncovering or equal effective areas of the piston faces of the two pistons, of a second hydraulic pump or motor of the same type which has its axially movable piston connected to and movable axially with but rotatable independently of the axially movable piston of the first pumpor motor and has its axially movable sheath connected to and movable axially with but rotatable independently of the axially movable sheath of said first pump or motor.

2. A hydraulic transmission comprising a gear pump and a gear motor, a common housing in which said pump and motor are enclosed, with the respective ears of the two arranged coaxially, a sheath associated with each of said gears, the sheaths for one pair of coaxial gears being held against axial movement and the gears bein axially movable together to sheath more of the pump ear and to unsheath more of the motor gear and vice versa, the other pair of coaxial gears being held against axial movement and the sheaths therefor being axially movable together to sheath more of the pump gear and to unsheath more of the motor gear and vice versa, said axially movable gears and axially movable sheaths being interlocked for axial movement together, whereby the volumetric capacities or displacements oi the pump and motor may be varied simultaneously in opposite directions.

19 3. A hydraulic transmission according to claim 2 in which the non-axially movable pair of coaxial gears are respectively connected to a drivlng shaft and a shaft to be driven.

4. A hydraulic transmission according to claim 2 in which the non-axially movable coaxial gears are connected, one to a driving shaft and the other to a shaft to be driven, and in which relatively movable clutch members are provided for clutching said shafts together when they have reached the same speed of rotation.

5. A hydraulic transmission according to claim 2 in which means extending to the exterior of the housing is provided for effecting simultaneous axial movement of the axially movable sheaths and of the axially movable gears.

6. A hydraulic transmission according to claim 2 in which by-passes permit displacement of operating liquid from one side of the axially movable parts to the other when varying the relative overall volumetric capacities or displacements.

7. In a hydraulic transmission, the combination with a rotary hydraulic pump or motor having two rotary intergeared pistons each provided with a close-fitting sheath relatively slidable axially to expose in eifective position more or less of the piston faces, an enclosing casing having intake and discharge ports and in which bearings for said pistons are carried, said casing providing space for simultaneous axial movement of one sheath while its piston maintains its position in said casing and axial movement of the other piston while its sheath maintains its position in said casing thereby to permit simultaneous covering or uncovering of equally efiective areas of the piston faces of the two pistons, of a second hydraulic motor or pump of the same type hydraulically connected to said first pump or motor to be driven by or to drive said first pump or motor, said second motor or pump having its axially movable piston connected to and movable with but rotatable independently of one of the axially movable parts of the first pump or motor and having its axially movable sheath connected to and movable with but rotatable independently of the other axially movable part of said first pump or motor.

MORRIS B. CARROLL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 711,662 Herdman Oct. 21, 1902 788,848 Riegel May 2, 1905 815,522 Fraser Mar. 20, 1906 1,647,621 Hawley Nov. 1, 1927 1,742,215 Pigott Jan. 7, 1930 1,870,824 Shepard Aug. 9, 1932 2,052,419 Moore et al. Aug. 25, 1936 2,079,375 McCollum May 4, 1937 2,149,326 Wilkin Mar. 7, 1939 FOREIGN PATENTS Number Country Date 448,953 Great Britain June 18, 1936 511,495 Germany Oct. 30, 1930 

